<!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" "http://www.w3.org/TR/html4/loose.dtd">
<html>
<!-- Copyright (C) 1999-2023 Free Software Foundation, Inc.

Permission is granted to copy, distribute and/or modify this document
under the terms of the GNU Free Documentation License, Version 1.3 or
any later version published by the Free Software Foundation; with the
Invariant Sections being "Funding Free Software", the Front-Cover
Texts being (a) (see below), and with the Back-Cover Texts being (b)
(see below).  A copy of the license is included in the section entitled
"GNU Free Documentation License".

(a) The FSF's Front-Cover Text is:

A GNU Manual

(b) The FSF's Back-Cover Text is:

You have freedom to copy and modify this GNU Manual, like GNU
     software.  Copies published by the Free Software Foundation raise
     funds for GNU development. -->
<!-- Created by GNU Texinfo 6.5, http://www.gnu.org/software/texinfo/ -->
<head>
<meta http-equiv="Content-Type" content="text/html; charset=utf-8">
<title>Interoperable Global Variables (The GNU Fortran Compiler)</title>

<meta name="description" content="Interoperable Global Variables (The GNU Fortran Compiler)">
<meta name="keywords" content="Interoperable Global Variables (The GNU Fortran Compiler)">
<meta name="resource-type" content="document">
<meta name="distribution" content="global">
<meta name="Generator" content="makeinfo">
<link href="index.html#Top" rel="start" title="Top">
<link href="Option-Index.html#Option-Index" rel="index" title="Option Index">
<link href="index.html#SEC_Contents" rel="contents" title="Table of Contents">
<link href="Interoperability-with-C.html#Interoperability-with-C" rel="up" title="Interoperability with C">
<link href="Interoperable-Subroutines-and-Functions.html#Interoperable-Subroutines-and-Functions" rel="next" title="Interoperable Subroutines and Functions">
<link href="Derived-Types-and-struct.html#Derived-Types-and-struct" rel="prev" title="Derived Types and struct">
<style type="text/css">
<!--
a.summary-letter {text-decoration: none}
blockquote.indentedblock {margin-right: 0em}
blockquote.smallindentedblock {margin-right: 0em; font-size: smaller}
blockquote.smallquotation {font-size: smaller}
div.display {margin-left: 3.2em}
div.example {margin-left: 3.2em}
div.lisp {margin-left: 3.2em}
div.smalldisplay {margin-left: 3.2em}
div.smallexample {margin-left: 3.2em}
div.smalllisp {margin-left: 3.2em}
kbd {font-style: oblique}
pre.display {font-family: inherit}
pre.format {font-family: inherit}
pre.menu-comment {font-family: serif}
pre.menu-preformatted {font-family: serif}
pre.smalldisplay {font-family: inherit; font-size: smaller}
pre.smallexample {font-size: smaller}
pre.smallformat {font-family: inherit; font-size: smaller}
pre.smalllisp {font-size: smaller}
span.nolinebreak {white-space: nowrap}
span.roman {font-family: initial; font-weight: normal}
span.sansserif {font-family: sans-serif; font-weight: normal}
ul.no-bullet {list-style: none}
-->
</style>


</head>

<body lang="en">
<a name="Interoperable-Global-Variables"></a>
<div class="header">
<p>
Next: <a href="Interoperable-Subroutines-and-Functions.html#Interoperable-Subroutines-and-Functions" accesskey="n" rel="next">Interoperable Subroutines and Functions</a>, Previous: <a href="Derived-Types-and-struct.html#Derived-Types-and-struct" accesskey="p" rel="prev">Derived Types and struct</a>, Up: <a href="Interoperability-with-C.html#Interoperability-with-C" accesskey="u" rel="up">Interoperability with C</a> &nbsp; [<a href="index.html#SEC_Contents" title="Table of contents" rel="contents">Contents</a>][<a href="Option-Index.html#Option-Index" title="Index" rel="index">Index</a>]</p>
</div>
<hr>
<a name="Interoperable-Global-Variables-1"></a>
<h4 class="subsection">6.1.3 Interoperable Global Variables</h4>
<a name="index-C-variable-interoperability"></a>
<a name="index-variable-interoperability-with-C"></a>
<a name="index-interoperability_002c-variable"></a>

<p>Variables can be made accessible from C using the C binding attribute,
optionally together with specifying a binding name.  Those variables
have to be declared in the declaration part of a <code>MODULE</code>,
be of interoperable type, and have neither the <code>pointer</code> nor
the <code>allocatable</code> attribute.
</p>
<div class="smallexample">
<pre class="smallexample">  MODULE m
    USE myType_module
    USE ISO_C_BINDING
    integer(C_INT), bind(C, name=&quot;_MyProject_flags&quot;) :: global_flag
    type(myType), bind(C) :: tp
  END MODULE
</pre></div>

<p>Here, <code>_MyProject_flags</code> is the case-sensitive name of the variable
as seen from C programs while <code>global_flag</code> is the case-insensitive
name as seen from Fortran.  If no binding name is specified, as for
<var>tp</var>, the C binding name is the (lowercase) Fortran binding name.
If a binding name is specified, only a single variable may be after the
double colon.  Note of warning: You cannot use a global variable to
access <var>errno</var> of the C library as the C standard allows it to be
a macro.  Use the <code>IERRNO</code> intrinsic (GNU extension) instead.
</p>



</body>
</html>
